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# Explanation of ENUM (RFC 2916) - PowerPoint PPT Presentation

Explanation of ENUM (RFC 2916). Patrik F ältström Area Director, Applications Area , IETF. Problem we want to solve. ENUM. 2. Problem statements. How do network elements (gateways, SIP servers etc) find services on the Internet if you only have a telephone (E.164) number?

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### Explanation of ENUM (RFC 2916)

Patrik Fältström

Area Director, Applications Area, IETF

### Problem we want to solve

ENUM

2

• How do network elements (gateways, SIP servers etc) find services on the Internet if you only have a telephone (E.164) number?

• How can subscribers define their preferences for incoming communications?

tel:+46-8-971234

mailto:paf@example.com

tel:+46-706051234

sip:paf@example.com

tel:+46-8-971234

mailto:paf@example.com

ENUM

tel:+46-706051234

tel:+46-706051234

sip:paf@example.com

Give this number to friends:

+46-8-971234

### Technical solution

ENUM

6

• Put domain names derived from telephone numbers in the global domain name system, DNS

• IETF ENUM Working Group created to solve the problem of using the DNS for:

• domain name in

• [Numbers re-formatted as domain names]

• URI out

• [mailto, sip, tel, http or other URI scheme]

• Solution: NAPTR records

• Use the URI’s for the communication

• take phone number

+46-8-6859131

• turn into domain name

1.3.1.9.5.8.6.8.6.4.e164.arpa.

• ask the DNS

mailto:paf@cisco.com

• return list of URI’s

sip:paf@cisco.com

Gateway

Sip server

ENUM use in more detail

Query

1.3.1.9.5.8.6.8.6.4.e164.arpa.?

Response

sip:paf@cisco.com

“Call setup”

Dial

+4686859131

Sip

sip:paf@cisco.com

Example

SIP-Server

SIP-Server

Internet

PSTN

Gateway

Gateway

Calling party

Called party

VoIP via SIP to VoIP

SIP-Server

“ENUM”

SIP-Server

Gateway

Gateway

VoIP via PSTN to PSTN

SIP-Server

“ENUM”

SIP-Server

Gateway

Gateway

NAPTR algorithm

Step 1

• Take an E.164 number and create a fully qualified domain name in a single highly defined and structured domain

• +46-8-971234

• +468971234

• 4.3.2.1.7.9.8.6.4.e164.arpa.

• Each digit can become a definable and distributed “zone” in DNS terms

• Delegation can (doesn’t have to) happen at every digit, including at last digit

• Zones such as country codes, area codes or primary delegated blocks of numbers can be delegated as well as individual numbers

• DNS defines authoritative name servers for NAPTR/service resource records

• Lookup NAPTR RR’s in DNS, and apply NAPTR/ENUM algorithm

4.3.2.1.7.9.8.6.4.e164.arpa.

!^.*\$!mailto:spam@paf.se!

!^+46(.*)\$!ldap://ldap.telco.se/cn=0\1!

• Use rewrite rules using regular expressions which operate on the E.164 number (+468971234)

• For ENUM, the NAPTR regexp field may yield an (unchanged) URL

• !<regexp>!<string>!

• “Match <regexp> on original E.164, and apply rewrite rule <string>”

^ - Match beginning

\$ - Match end

. - Match any character

.* - Match any number of any character

() - Grouping, \n in <string> is replaced with group number ‘n’ in <regexp>

• \$ORIGIN 4.3.2.1.7.9.8.6.4.e164.arpa.

• IN NAPTR 10 10 ”U” ”mailto+E2U” ”!^.*\$!mailto:spam@paf.se!”

• IN NAPTR 20 10 ”U” ”ldap+E2U” ”!^+46(.*)\$!ldap://ldap.telco.se/cn=0\1”

• Note that no line break should be in the records

• RFC 2916 published in September 2000

• The domain e164.arpa delegated to RIPE NCC

• RIPE NCC appointed by the IAB according to RFC 2916

• ITU SG2/WP1/2 liaison statement:

• Member state can inform ITU on entry of numbers in ENUM tree

• Instructions to RIPE NCC

• Any “request” not coming from TSB is to be forwarded to TSB

• If TSB says no, no delegation is to be done

• All evaluation of any “request” is to be done by TSB

• RIPE NCC is only creating and evaluating the technical data which they need for the actual delegation

• RIPE NCC is to communicate with TSB

• RIPE NCC is to make public any communication regarding a “request”

• Delegation of domains below e164.arpa to managing entities that are appointed by member states

• A few “requests” have been passed to TSB, which have responded very quickly

• National issues are not resolved

• We have not heard that issues related to verification of holder of E.164 number are resolved anywhere

### Issues

• The DNS requires a unique root

• More on this later

• In DNS, we have a question on how to have competition in general, since one commercial company “had too large a market share”

• Competition for registrations of DNS records is ensured using a registry/registrar model:

• One registry which runs the DNS server

• Competition at this level is handled when choosing the registry, because that can only be one organization

• Many registrars which the customer talk with

• Registrars decide for example price for a registration

• Why is a unique root used in ENUM?

• Say I have phone number +468971234

• I can choose between a.com and b.com

• I choose b.com, and get the DNS domain

• 4.3.2.1.7.9.8.6.4.b.com.

• Axel is to call me

• He knows my phone number, +468971234, only

• How is he to know that it is in b.com and not a.com I have my data?

• General issues in RFC 2836

• We need a “Golden Tree” for E.164 numbers

• Address and Routing Parameters Area

• See contribution from ISOC

• See http://www.iana.org/arpa-dom/

• ip6.arpa

• e164.arpa

• E.164 numbers

• The implementation of a globally unique ENUM tree provides ample opportunity for competition at the national level

• Having ENUM using domain e164.arpa means that one still have:

• Ability to have dialing plans in other domains

• Competition regarding registration according to registry/registrar model on all levels in DNS tree

• Competition when selecting the registries

• Competition regarding services

• A user very seldom dial an E.164 number on his phone

• Inside Cisco, people dial 58509 to me

• Outside Cisco, from Sweden, people must dial 0014085258509

• Not all dialed numbers are E.164 numbers

• People use dialing plans

• Dialing plan information can be resolved by the use of same technology as ENUM

• A registry runs the DNS server for a specific domain name

• one domain -> one registry

• A customer contacts a registrar when he want to have things registered, not the registry

• Registrar verify customer data, do billing, and send data to registry when delegation is to be done, changed or cancelled

See next slide…

• Registries are needed which runs the DNS

• On a country code level

• Inside a country code, according to local policy

• The model we use today with DNS is

Holder of a domain

Registry

Registrar

Registrar

Registrant

Holder of a domain

Registrar

• A customer in ENUM announces what services he subscribes to

• Examples:

• Email

• Web homepage

• SIP service (VoIP)

• Telephony

• Each one of these services can be handled by separate contracts between customer and service provider

• These contracts have nothing to do with the announcement via ENUM of their existence

RIPE-NCC

IETF/IAB

ITU-T TSB

Registry for country

Registrar for country

Registrar for country

Registrar for country

ENUM Service provider

ENUM Service provider

Service provider

for email

ENUM Service provider

Service provider

for email

Service provider

for email

Service provider

for telephony

Service provider

for telephony

Service provider

for telephony

Customer

paf@cisco.com